The invention concerns a tensioning device for the cable of a window lifter of a vehicle.
It is known to the state of the art to fasten the two cable ends of the window lifter to the drive bracket and thereby to pull this drive means up and down a guide rail. However it is inevitable during the operation of the window lifter that the cable shall gradually stretch and thereby that play will arise in this cable connection, this play making itself felt when the window lift is actuated, for instance by a crank as a dead zone. It is further known to mount a cable-tensioning device at the drive bracket so that the cable stretching is compensated by a spring. Such a tensioning device is disclosed in West German Patent 37 37 733 and U.S. Pat. No. 4,235,046 the disclosures of which are incorporated herein by reference.
However cable stretching appears in cable window lifters not only as an aging effect but it also may arise when the window moves into its upper end position, wherein the drive bracket comes to rest against a stop, excessive force is applied to the crank to artifically elongate the "upper" cable segment between the cable drum and the drive bracket or the guide rail becomes so warped that cable slack arises between the cable drum and the drive bracket. Such cable slack disappears once the window is moved down. Therefore the tensioning device may not become operative when such a spurious, mostly slight cable elongation takes place.
However the known tensioning devices also compensate for such artificial cable elongations. As a result, the cable system for all its ensuing service life is harder to operate, at least until a real cable elongation eliminates this tension.